Sonic 0

All the samples were prepared using austenitic chromium-nickel steel AISI 304 (1.4301 according to the EN10088-1 standard) in the form of 10 × 20 mm plates as a substrate. Before the deposition of carbon nanotubes (CNT) layer the mechanical and chemical cleaning was performed. It included the following steps: abrasive sandpaper grinding (600 grit), sonication in acetone (≥ 99.5%, Avantor Performance Materials, Poland) and then in ethanol (≥ 96%, Avantor Performance Materials, Poland) for 5 min each using the ultrasonic bath (Sonic-0.5, Polsonic, Poland). Cleaned plates were stored in ethanol and dried just before the preparation of CNT layer.

Wet gluten was obtained according to the Polish Standard [16 ]. Gluten samples (2 mm thick) were put on the Petri dish floating on the surface of the ultrasonic scrubber. Samples were sonicated for 300 s in an ultrasonic scrubber Sonic-0.5 (POLSONIC Palczyński Sp. J., Warsaw, Poland) using 40 kHz ultrasound at 80 W. The effectiveness of the ultrasound was checked by observing holes in the aluminum foil caused by the cavitation.

CNT after chemical oxidation were added to the 2:1:1 (v/v/v) mixture of acetone (≥ 99.5%, Avantor Performance Materials, Poland), ethanol (99.8%, Avantor Performance Materials, Poland) and distilled water. The 1 mg/mL solution was sonicated for 5 min using Sonic-0.5 (Polsonic, Poland) ultrasonic bath to improve the CNT dispersion. The process of EPD of CNT on stainless steel plates was performed using the custom-made equipment with PLH250 (Aim-TTi, United Kingdom) DC power supply. Three electrodes arrangement was applied including two counter electrodes with a distance of 15 mm as cathodes and the substrate mounted in a holder symmetrically between them as an anode. The CNT solution was poured into a polypropylene vessel prepared by Fused Deposition Modeling (FDM) 3D printing. For this, 1.75 mm polypropylene filament (Verbatim, Japan) and UBOT 3D S+ (UBOT 3D, Poland) 3D printer were used. The vessel dimensions were designed to fit to the geometry of the applied electrodes arrangement and therefore to reduce the consumption of the solutions. All CNT layers were prepared in the process of EPD using the voltage of 30 V for 60 s. Then, the samples were dried in a room temperature.